As expected, John Kerry, the senior senator from Massachusetts and former Democratic presidential candidate in 2004, has been nominated by President Obama to replace Hillary Clinton as secretary of State in Obama's second term.

Kerry is popular in the Senate on a bipartisan basis. His confirmation should present few issues, especially since he has already gone through the even more severe vetting process of an intense and highly competitive presidential race.

And because of his detailed knowledge of many foreign policy issues, due to his chairmanship of the Senate Foreign Relations Committee over the years, not to mention his presidential aspirations and his Vietnam military service at an earlier stage in life, he is also well placed to ensure thoughtfulness and continuity in American foreign policy in the months ahead.

Like Clinton, Kerry is diligent, hardworking, patient and pragmatic. Like her, while not necessarily personally close to President Obama at the outset of his Cabinet service, he is certainly on friendly and collegial terms with the commander-in-chief. He has been seasoned by the frustrations of dealing in intractable foreign policy issues for many years, yet is still idealistic and visionary on issues ranging from climate change to Middle East peace to global development.

Once confirmed, Kerry's challenge will be to help the president navigate some very demanding shoals in the four years ahead. They may be tougher than those the president had to face in his first four years.

In Obama's first term, there were big decisions to be sure, and the administration handled most of them reasonably well. Even though the Afghanistan war has proved frustrating, Obama showed tenacity in tripling U.S. combat forces there for a time, and expanding aid to neighboring Pakistan as well (through a law that Kerry co-sponsored in the Senate). Even though Obama failed to negotiate a way to keep U.S. forces in Iraq a little longer as desired, the president and his team were still careful in how they executed America's departure from that controversial conflict.

Meanwhile relations were improved -- at least somewhat -- with Russia, a welcome development. In turn, relations were toughened at least somewhat with China, a necessary development under the circumstances. Policies that led to the killing of Osama bin Laden and Moammar Gadhafi in Libya were well handled, too.

But harder choices may soon loom, presenting complex diplomacy for the president, and Kerry:

Syria now represents a far deadlier and more intractable conflict than Libya and it is not clear that we can really continue to keep our hands largely off this mess, given its importance in the broader Middle East. Nor will the Libya model of intervention work in this much more populous country.

A little tougher stance with China through the so-called Asia "rebalancing" was the right policy for Obama's first term, as Beijing had become too assertive. But now is the time to make sure this firmer American line does not lead to another Cold War.

Now that Vladimir Putin is back in the Kremlin, finding a way to work with him again will be much harder than was Obama's earlier success at repairing U.S.-Russian relations with President Dimtry Medvedev.

In Iraq, we could afford to leave (even if it might have been better that we stayed with a modest presence) because Iraqis havenow formed a strong state. But in Afghanistan, we probably need to find a way to stay, as it is doubtful that the weak Afghan state can really survive totally on its own.

When it came to the budget, predecessors, Colin Powell, Condoleezza Rice and Hillary Clinton had it easy. They presided over diplomacy and development budgets when federal spending was rising. Kerry will have to protect core capabilities as his budgets are cut.

Most of all, possible war looms with Iran. Attacking Iran's nuclear facilities (with or without Israeli participation) would be a substantially more monumental decision than tripling combat forces in Afghanistan, authorizing the raid against bin Laden, using force against Gadhafi in Libya, or leaving Iraq.

Kerry, a Vietnam vet who is tough but who also knows firsthand the horrors of war, will be an important adviser to President Obama as this choice is perhaps directly confronted in the year or two ahead.

Alas, at that point the honeymoon with his Senate colleagues could be over, the politics could be rougher, and the stakes will surely be very high. All the more reason why someone with Kerry's stature and experience in Congress are needed. The president has found a good man for a very difficult job.